It added: "We are only in a first stage of information gathering at the moment and it is too early to speculate on whether this could lead to any specific state aid investigations."

Earlier, the Financial Times reported that the Commission had requested details of assurances given to several specific companies, including Apple and Starbucks.

The Department of Finance said it received queries from the Commission "from time to time" on a range of issues including tax, but said that "Ireland operates an open, transparent and statute based taxation system".

A US Senate committee accused Ireland of acting as a conduit for Apple's earnings so it could sidestep large tax payments around the world - a charge Ireland strongly rejected.

EU state aid rules are designed to prevent unfair practices, although it is not clear that countries offering favourable tax terms to companies or industries would violate such rules.

While a preliminary step, the move by the European Commission, the EU's competition authority, forms part of wider efforts by European and US authorities to shed more light on international tax policy.

Depending on what the requests for information produce, a formal investigation could follow.

"The Commission is simply gathering information about tax rulings. Requests for information have been sent to several member states," Antoine Colombani, the European Commission's spokesman on competition issues, said.

The Commission's move follows revelations about the tax-planning practices of major corporations such as Apple, Google and Starbucks that have allowed the companies to pay minimal tax despite multi-billion dollar revenues and profits.

Ireland, the Netherlands and Luxembourg all have specially structured corporate tax arrangements, but so do other EU member states. In the majority of member states, the effective corporate tax rate is nearly always lower than the nominal rate, which is usually the result of "sweeteners" in the tax code.

Ireland said it was not aware of any formal state aid inquiry by the Commission and said it had an open and transparent tax system.

"Ireland, like all member states, from time to time receives queries from the Commission on a variety of issues, including tax, and we always cooperate fully with such requests," the finance department said in a statement.

Officials from Luxembourg were not immediately available to comment.

A spokesman for the Dutch finance ministry said: "In general we do get enquiries [from Brussels] about all kinds of matters, about tax matters, finance ministry matters, quite often, but these are confidential."

'Strong response needed from Government'

Fianna Fáil Finance Spokesperson Michael McGrath has said the Commission's decision to launch a preliminary investigation proves that the Government has been complacent on the issue.

Mr McGrath said the committee proceedings in the US and the UK on the issue have been taken more seriously by the European authorities than by the Government.

It is a significant and in many respects an unwelcome development, he said, adding that a strong and decisive response is needed from the Government.

He said it is an opportunity for the country to demonstrate that it has a transparent tax system that treats all companies and taxpayers equally and he hopes that is the outcome of the preliminary investigation.

He also said there is no evidence of dodgy deals, adding that the Government, the Department of Finance and the chairperson of Revenue have all said that no deals have been done with individual companies.

He added that he would like to know if any formal complaints against Ireland had been lodged with the Commission.